What Is a Centrifugal Concentrator?
Centrifugal Concentrators are devices that apply centrifugal force to a sample in solution under reduced pressure to evaporate the solvent and concentrate the sample.
It generally consists of a centrifugal chamber, a cooling chamber and a decompression unit.
Uses of Centrifugal Concentrators
Centrifugal Concentrators are characterised by lowering the boiling point of the solvent in the sample during concentration and by applying centrifugal force to the sample to prevent solvent ejection, foaming, etc. This means that sample loss due to heating or boiling can be reduced, making it suitable for the concentration of samples for microanalysis where very small quantities of sample are used.
They are used to concentrate DNA, RNA and peptides, and to prepare other applications requiring concentration and drying. They are also used in many areas for the concentration of solvent and water mixtures, residue analysis, toxicological investigations and forensics, combinatorial chemistry, food analysis and environmental analysis.
Principle of Centrifugal Concentrators
Centrifugal Concentrators used for microanalysis and other applications are characterised by the use of the ‘three states of matter’ to concentrate samples. Specifically, the solvent in the sample is evaporated under reduced pressure at a lower temperature than under atmospheric conditions, vaporised and collected, and the sample is concentrated by reducing the amount of solvent in the sample. Therefore, the minimum configuration required for a Centrifugal Concentrator is a centrifugal chamber, a cooling chamber and a pressure reducing device such as a vacuum pump.
In Centrifugal Concentrators, the centrifugal chamber is depressurised using decompression device while the liquid sample is inside the centrifugal chamber. The reduced pressure lowers the boiling point of the substance, and consequently, the boiling point of the solvent within the sample placed in the centrifugal chamber is also reduced. Solvent evaporation is therefore possible at lower temperatures than under atmospheric conditions.
The evaporated solvent moves to the cooling chamber, where it is cooled and collected. At this point, the sample is heated, which promotes solvent evaporation and prevents the solvent freezing that occurs during depressurisation. The pressure at the sample surface in the centrifuge chamber is the same as in the depressurised centrifuge chamber. At this time, the Centrifugal Concentrator applies centrifugal force to the sample, which causes a pressure gradient inside the sample where the pressure is higher the deeper it goes.
Therefore, when the pressure within the centrifugal chamber is carefully controlled, only the surface layer of the sample experiences a lower boiling point due to the reduced pressure. This results in surface boiling without affecting the interior of the sample, effectively preventing eutectic boiling, which occurs when the interior of the sample undergoes boiling.
Other Information on Centrifugal Concentrators
1. Sludge Concentration by Centrifugal Concentrator
Centrifugal Concentrators are mainly used in fields such as microanalysis, but in recent years they have also been used in sewage sludge treatment. Among sewage sludge, sludge from the first settling basin settles easily and can be easily thickened by gravity settling.
However, sludge in the final sedimentation basin (especially excess sludge) does not settle easily, making it difficult to concentrate the sludge by gravity settling. Centrifugal Concentrators are therefore used as a type of mechanical sludge thickening method (mechanical thickening method). Mechanical thickening methods also include atmospheric pressure floating thickeners and belt-type filtration thickeners.
2. Structure and Operation of Centrifugal Concentrator for Sludge Concentration
Centrifugal Concentrators for sludge concentration concentrate excess sludge by centrifugal force. At this time, no depressurisation is carried out. Centrifugal Concentrators for sludge thickening have a structure in which the outer body and the inner body with screw rotate around the sludge feed pipe while maintaining a certain difference in rotation between them.
This rotational difference is set to be, for example, three to eight revolutions, with the inner cylinder with the screw rotating slightly slower. The sludge is first fed into the outer cylinder through the sludge feed pipe of the Centrifugal Concentrator. Before the sludge is fed to the Centrifugal Concentrator, flocculants or other agents are generally added.
The outer cylinder rotates at high speed and the sludge is subjected to centrifugal force, causing sedimentation and separation due to the difference in specific gravity between water and solids, resulting in the accumulation of thickened sludge in the outer cylinder. At this point, there is a difference in rotation between the inner and outer cylinders, with the inner cylinder rotating slightly slower, so the deposited concentrated sludge is scraped off and pushed out by a screw attached to the inner cylinder and discharged.
Such Centrifugal Concentrators can, for example, be used to concentrate sludge with a concentration of 1% or less into a concentrated sludge of 4-6%.